A steering railway bogie includes a frame and two or more wheelsets connected to the frame. The frame is connected to a railway vehicle body. Each wheelset comprises two spaced apart wheels operatively linked by an axle. The wheelsets have freedom of movement to yaw relative to other wheelsets of the bogie so as to give an angle of steering.
Each wheel often has a flange for safety but they rarely make contact with the rail. The tread of each wheel is slightly tapered having a non linear conical profile. The purpose of steering bogies is to minimise creep forces other than traction creep forces at the wheel rail contacts and to evenly distribute the lateral curving forces between each wheelset to minimise wheel, rail and track damage.
When a steering bogie encounters a bend, the wheelsets displace laterally on the rail so that the outer wheel has a higher contact angle to the rail relative to the inner wheel causing the normal contact force of the wheelset on the rail to have a lateral component to the cross level of the rails. If the wheels of the wheelsets have dependent rotation there will also be longitudinal creepage differences between the wheels due to differences in rolling radius that generate a net yaw moment on the wheelset from creepage forces. Further to this a steering bogie wheelsets will displace relative to each other to produce a steering angle and the bogie frame will displace in yaw rotation to maintain tangential alignment of the bogie to the track. In constant curvature track, the steering angles between wheelsets and the yaw rotation angle for the bogie which produce radial alignment of the wheelsets, are a fixed ratio.
Previous steering bogie designs such as yaw relaxation, self steering, force steering, articulated steering and actuated wheelset yaw did not control the yaw rotation of the bogie but were reliant on creep force to correct the bogie yaw. Under traction with low friction to adhesion ratios such bogies are unable to control the bogie yaw.
Passive steering bogies such as yaw relaxation and self steering are fully reliant on creep forces to actuate the steering of axles and under high traction forces revert to straight alignment. Force steering and articulated steering bogies are partially reliant on creep forces for actuation and suffer partial steering lose under high tractions.
Actuated wheelset yaw bogie designs require sensor inputs and control which are independent of the wheel rail creep forces, to control the steering angle of the wheelsets under traction with low friction to adhesion levels. Actuated wheelset yaw bogie designs require the placement of yaw actuators and sensors on the bogie frame or across the bogies primary suspension. These locations are subject to higher impact loads during train operations than is experienced at or above the secondary suspension requiring more robust equipment.